We performed a search of the PubMed database including several interrelated queries (e.g., “phodiesterases” OR “PDE” AND “inflammation” OR “autoimmunity”; “apremilast” OR “PDE4 inhibitors” AND “psoriatic arthritis” OR “inflammatory bowel diseases” OR “ulcerative colitis” OR “enteropathic spondyloarthritis”). Here, PDE4A is linked to inflammatory bowel disease.